Carburetor flow stand

ABSTRACT

Flow-testing apparatus and methods for determining air-fuel ratios of a carburetor. An air flow is established through a carburetor and fuel containing a tracer material is supplied to the carburetor. Means, e.g., an infrared radiation analyzer, is provided for detecting tracer material in the air-fuel mixture flowing from the carburetor and oxygen detector means detects the concentration of oxygen. Analog divider circuitry serves as means for deriving from the detected tracer and oxygen concentrations the air-fuel ratio produced by the carburetor. Arrangements are disclosed for improving the response of the radiation analyzer by providing increased rate of flow of sampled gas through the analyzer and also for cancelling infrared radiation absorption interference caused by vaporized fuel in the analyzer.

United States Patent 11 1 Bordeaux CARBURETOR FLOW STAND [76] Inventor: Jenn Bordeaux, 2840 N. Spring, St.

Louis, Mo. 63107 [22] Filed: Aug. 15, 1972 [21] Appl. No; 280,788

[52] US. Cl. 73/118 [51] Int. Cl. 601m 19/00 [58] Field of Search 73/116, 118

[56] References Cited UNITED STATES PATENTS 3,469,442 9/1969 Brueckner 73/118 3,456,500 7/1969 Zaske 2,734,381 2/1956 Jacobson 73/118 UX Primary Examiner-Jerry W. Myracle Attorney-Peter S. Gilster et al.

[ 1 June 26, 1973 [57] ABSTRACT Flow-testing apparatus and methods for determining air-fuel ratios of a carburetor. An air flow is established through a carburetor and fuel containing a tracer material is supplied to the carburetor. Means, e.g., an infrared radiation analyzer, is provided for detecting tracer material in the air-fuel mixture flowing from the carburetor and oxygen detector means detects the concentration of oxygen. Analog divider circuitry serves as means for deriving from the detected tracer and oxygen concentrations the air-fuel ratio produced by the carburetor. Arrangements are disclosed for improving the response of the radiation analyzer by providing increased rate of flow of sampled gas through the analyzer and also for cancelling infrared radiation absorp-' tion interference caused by vaporized fuel in the analy- Z61.

30 Claims, 4 Drawing Figures v MONITOR CIRCUITRY RECORDER ANALOG DIVIDER PATENIEBJIIIZG Ill mums F|G.l

MONITOR MONITOR CIRCUITRY ANALOG DIVIDER PLENUM PATENIEU M26 I973 SHEET 2 0F 3 FIGZ CIR

PRESSURE CUITRY COMPENSATION CIRCU ITRY EVAPOR ATOR CIR OXYGEN DETECTOR CUITRY RAD. ANAL. CELL TRACER DETECTOR CI RCUITRY ANALOG DIVIDER BACKGROUND OF THE INVENTION This invention relates to carburetor flow-testing and more particularly to improved apparatus and methods of flow-testing carburetors for determining air-fuel ra tios.

In the manufacture of carburetors, it is an industrywide practice to place each manufactured carburetor on a flow stand to quantitatively measure the amount of air and fuel being handled by the carburetor at various throttle settings such as fully closed (curb idle), slight throttle (off idle), part throttle and wide-open throttle.

From such measurements, so-called air-fuel ratios of the air-fuel mixture produced by the carburetor can be determined automatically or mathematically. By airfuel ratio (sometimes referred to as fuel-air ratio) is meant the ratio of the quantity (weight) of air flowing through the carburetor per unit time to the quantity (weight) of fuel flowing through the carburetor per unit time during operation of the carburetor.

In the prior art, the quantity of air has been measured after the air-fuel mixture leaves the carburetor and after the fuel has been separated from the air by means such as orifice meters, venturi meters, and so-called sonic nozzles. Measurement of the quantity of fuel is carried out in such prior art by metering the fuel as it enters the carburetor, as by means of a positive displacement meter. Examples of the prior art include Converse III et al. US. Pat. No. 3,517,552 and references cited therein.

The copending application of E. H. Casey, Ser. No. 158,801, filed July l, 1971, and entitled Carburetor Flow Stand, discloses measuring of air and fuel quantities downstream of the carburetor by sensing a property of the fuel, providing for more rapid measurement ofthe fuel quantity and thus more rapid readout of airfuel ratios. In one embodiment disclosed in said application of E. H. Casey, the property of the fuel which is sensed is a tracer material contained in the fuel.

In the copending application of Jean Bordeaux, Ser. No. 158,796, filed July 1, 1971, and entitled Carburetor Flow Stand, there is disclosed a carburetor flow stand in which a tracer material previously added to the fuel is vaporized from the air-fuel mixture and is detected with an infrared analyzer or spectrophotometer. The tracer is one having a high absorption characteristic in the infrared spectrum.

It has been found that one limitation of a flow stand as disclosed in said application of Jean Bordeaux is that several seconds may be required for the infrared analyzer to respond to changes in the air-fuel ratio since a short period is required for the gas mixture being sampled to fill the sample tube of the analyzer. Thus the flow stand does not operate in a truly dynamic manner, i.e., in a manner in which changes in the air-fuel mixture produced by a carburetor under test are dynamically indicated. As a result, more time is required in flow testing of a carburetor than is desired.

Another problem which has been found to occur in the determination of fuel-air ratios by infrared radiation analysis is one which results from absorption interference during analysis caused by the pressure of fuel in vapor form in the analysis or sample cell. While such interference can be reduced to some degree by the use of certain conventional filter techniques, its presence is nonetheless objectionable.

SUMMARY OF THE INVENTION Among the several objects of the invention may be noted the provision of improved carburetor flowtesting apparatus, i.e., a carburetor flow stand, and methods for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof; the provision of such apparatus and methods providing greatly increased accuracy and speed in determining such air-fuel ratios, and in which such determination is substantially dynamic; and the provision of such apparatus and methods employing infrared radiation analysis, i.e., infrared detection of a tracer material in the fuel but minimizing the effects of radiation absorption interference during the radiation analysis so as to provide increased accuracy and repeatability of results.

Briefly, improved carburetor flow-testing apparatus according to the invention comprises means for establishing flow of air through a carburetor under test and means for supplying fuel to the carburetor for causing it to produce flow of an air-fuel mixture. The air-fuel mixture passes to evaporator-separator means for evaporating the tracer material and separating liquid fuel from the mixture, providing an air flow including tracer vapor. An infrared radiation analyzer samples the air flow and detects the partial pressure of the tracer in the air flow and pressure detector means detects the partial pressure of the air in the air flow. Means, preferably an analog divider, derives from these detected partial pressures the air-fuel ratio produced by the carburetor.

In one embodiment, a polarographic sensor detects the partial pressure of oxygen in the air flow so as to determine air quantity. In this embodiment, provision is made for increased rate of sampling flow to improve speed of response for substantially dynamic testing.

An improved infrared indication detector embodiment of the invention is described which substantially cancels the effects of radiation absorption interference from fuel vapor remaining in the air flow from the evaporator-separator.

An alternative embodiment of the reducedinterference detector provides for extremely rapid sampling to achieve substantially dynamic testing.

Other objects and features will be in part apparent and in part pointed out hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram, in partly blockdiagram form, of a flow-testing apparatus constructed according to the present disclosure;

FIG. 2 is a similar schematic diagram of the presently disclosed flow-testing apparatus; and

FIGS. 3 and 4 represent in cross section two infrared radiation detection arrangements useful in the apparatus of FIGS. 1 and 2.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, and more particularly to FIG. 1, carburetor flow-testing apparatus of the present invention is illustrated. The apparatus includes a carburetor flow stand indicated generally at 11 on which is adapted to be mounted a carburetor, as depicted at 13, for flow-testing (or so-called flowing) of the carburetor under conditions representative of normal operation thereof. While carburetor 13 is shown in outline form only, it will be understood that it contains the usual fuel bowl and float mechanism, together with an automatic choke, idle and high-speed fuel systems, as well as a conventional throttle valve.

Liquid fuel, including a tracer material as described hereinbelow, is supplied to carburetor 13 from a fuel tank 15 containing a volume of fuel 16 by a fuel line 17 connected to the carburetor. Fuel line 17 includes a valve 19 for controlling the supply of fuel, which is maintained by a pump 21 and pressure regulator valve 23 at a predetermined pressure indicated by a pressure gauge 21. Fuel is withdrawn from fuel tank 15 by pump 21, and discharged into a pipe loop 27 which recirculates the fuel to the tank 15. Pipe loop 27 preferably includes a number of so-called drops which supply the fuel to other carburetors, Fuel line 17 may be considered one of such drops. Recirculation of the fuel to tank 15 is preferably of a flow rate adequate to insure agitation of the fuel 16 in the tank and thereby to insure uniform mixing of the tracer with the fuel. A conventional stirrer in tank 15 may instead be employed, if desired. Tank 15 includes a floating cover or head 29 for minimizing vapor space over the fuel which might otherwise upset the relative balance of the tracer and fuel from evaporation.

Installed in pipe loop 27 in a monitor or detector 31 for detecting the quantity of the tracer in the fuel. This detector'may, for example, comprise an infrared absorption analyzer which, in conjunction with certain electronic monitor circuitry 33, provides a signal on a lead 35 which varies as a function of the percentage of the tracer in the fuel. It will be noted that the signal on lead 35 could be used to drive a meter or other indicator device, thereby to visually indicate the percentage of tracer in fuel 16, or could be used to regulate automatically the addition of fuel or tracer to tank 15, thereby to maintain a concentration of tracer in fuel 16 at a predetermined level.

While the fuel 16 in tank 15 may be gasoline, it is preferred to use a fuel which is much less volatile, such as Stoddards solvent (having a flash point of about 100 F in order to reduce significantly the possibility of fire or explosion during operation of the flow stand.

A suction line 37 is provided for causing air to be drawn through carburetor 13. For this purpose, suction line 37 conventionally communicates with a local vacuum source represented in the drawings by a vacuum pump 39 and is interconnected with a suitable plenum chamber 41 of the test stand by means of a plurality of suction branches 43. Each suction branch 43 includes a so-called sonic nozzle 45 in series with a control valve 47. Air is thus drawn through carburetor 13, through a separator-evaporator 49 and thence through a pair of conduits 50a and 50b into plenum chamber 41, and finally through one or more of the sonic nozzles 45, depending upon the positions of control valves 47. Thus it is seen that the test stand provides a ducting arrangement interconnecting the downstream side of the carburetor with the vacuum source and by means of which air is drawn by the vacuum source through the carburetor.

Sonic nozzles 45 are each of the type described in detail in the aforementioned Converse et al. U.S. Pat. N 0. 3,517,552 and referred to therein as a critical flow venturi meter. Such a nozzle is characterized by operation such that the pressure upstream of the nozzle is directly proportional to the volumetric flow rate of the air flowing through the nozzle so long as the pressure drop across the nozzle exceeds a predetermined magnitude, occurring at sonic velocities. Accordingly, the pressure in plenum chamber 41 is a direct function of the air volume flowing per unit of time through nozzles 45 and thus through carburetor 13. This pressure in plenum chamber 41 is detected by a conventional pressure detector or transducer 51. Detector 51 is interconnected with suitable circuitry 52 or conversion means for converting the pressure variations sensed by transducer 51 so as to drive a meter or gauge 53. Gauge 53 may be calibrated directly in air volume or weight units to provide a convenient reading thereof during operation of the flow stand.

For purposes of the present description, carburetor 13 may be assured to be a multithroat type, such as a so-called four-barrel carburetor having two sides, each with a main and an auxiliary throat or venturi. In such a carburetor, each side contributes to the air-fuel mixture produced by the' carburetor. In testing such a fourbarrel carburetor, it ordinarily may be sufficient (as assumed herein) to be able to determine the air-fuel ratio of the air-fuel mixture produced by each side of the carburetor.

Accordingly, evaporator-separator 49 (hereinafter referred to simply as an evaporator) is constructed so that it has two symmetrically identical halves 55aand 55b for dividing the air-fuel mixture from carburetor 13 into two halves or streams corresponding to the throats of each side of the carburetor. Thus, side 55a of evaporator 49 receives the air-flow mixture from the main and auxiliary throats of one side of the carburetor and side 55b receives the air-fuel mixture flowing from the other side of carburetor 13. However, it instead may be desirable in some circumstances to determine the airfuel ratio of the mixture produced by each of the plurality of throats. In that event, it will be understood that the air-fuel mixture flowing from the carburetor would be divided into streams corresponding respectively to each of the throats.

Each side of evaporator 49, represented in the drawings as a chamber in cross-section, the two sides of chambers 55a and 55b being defined by a partition 56, includes suitable baffles as indicated at 57 for causing evaporation of the tracer material from the liquid fuel flowing from carburetor 13 as well as separation of the liquid fuel from this mixture. Hence, an air flow is provided from each side of the evaporator which is substantially free of liquid fuel but which includes the tracer material in gaseous form. The partial pressure of the tracer material in this flow from each side of evaporator 49 varies as a function of the air-fuel ratio of the air-fuel mixture produced by the throats of the corresponding side of carburetor 13. A drain provision 58 including a valve connected with drain lines at the bottom of the evaporator permits draining of the separated fuel.

In accordance with the invention, individual infrared gas analyzers 59a and 59b are employed to detect the partial pressure of the tracer material in the air stream flowing from the respective sides 55a and 55b of evaporator 49 through conduits 50a and 50b, respectively. Associated with the infrared analyzers are respective pressure detectors 61a and 61b for detecting pressure associated with the air flowing in each of the streams from evaporator 49. I.e., pressure detectors 61a and 61b effectively detect the pressure of and thereby the quantity of the air of the gas mixture flowing through the respective conduits 50a and 50b.

Pressure detectors 61a and 61b may simply be responsive to absolute air pressure or instead they may be responsive to the partial pressure of oxygen in the air. In either case, they may be said to detect or be responsive to the partial or absolute pressure associated with the air in the respective air streams flowing from the evaporator. Specifically, detectors 61a and 61b each generate a signal proportional to the mass flow rate of air flowing through sample lines 67a and 67b, respectively, and thus serve as means for detecting the quantity of air flowing per unit of time from the respective sides of the evaporator.

Respective circuits 63a and 63b are analog dividers functioning as means for comparing the partial pressure of the tracer material, as detected by the respective analyzers 59a and 59b with the partial pressure associated with the air, as detected by. pressure detectors 61a and 61b, in respective ones of the two streams flowing from evaporator 49. Each of the means 63a and 63b derives from the compared pressures an air-fuel ratio produced by the throats of each of the two sides of the carburetor. These air-fuel ratios are indicated by meters 65a and 65b or other analog readout means.

The tracer material in fuel 16 is preferably a'compound selected from one of the halogenated hydrocarbons and preferably one of the compounds such as dichlorodifluoromethane, dichlorotetrachloromethane, dichloromethane, dibromotetrafluoroethane and trichlorotrifluoroethane. The last-mentioned compound, a fluorocarbon sold under the trademark Freon 113, is a nonflammable, nontoxic, low boiling point, volatile material having a high infrared absorption characteristic at a location in the infrared spectrum where Stoddards solvent has a relatively low absorption characteristic. The useof the latter compound is preferred and is added to fuel 16 in a predetermined percentage such as 1%. Thus the air-fuel mixture flowing from carburetor 13 is such that the fuel of that mixture contains this tracer material in the predetermined percentage. Evaporator 49 causes substantially complete evaporation of this tracer material from the liquid fuel (such as Stoddard s solvent) separating the liquid fuel from the air-flow mixture such that the air flowing from each of the two halves 55a and 55b of evaporator 49 includes this tracer material in gaseous form.

Considering the infrared analyzer portion of FIG. 1 now more specifically, a portion of the air flowing from each half 55a and 55b of evaporator 49 is withdrawn through sampling probes 68a and 68b extending into conduits 50a and 50b, respectively, and thence through sampling lines or conduits 67a and 67b. These sampling lines or conduits are interconnected with a valve 69 having a normal position in which conduit 67a communicates with a further conduit 71a and conduit 67b communicates with a further conduit 71b, and a reversed position in which conduit 67a communicates with conduit 71b and conduit 67b communicates with conduit 71a. Thus the conduit connections can be reversed through operation of valve 69 for purposes explained hereinbelow. Conduits 71a and 71b supply the withdrawn air including the gaseous tracer to respective sample cells 73a and 73b of infrared analyzers 59a and 59b. Conduits 75a and 75b interconnected with vacuum line 37 or a conduit 77 and with sample cells 71a and 71b, respectively, draw the air and tracer material through the sample cells.

Associated with each of sample lines 67a and 67b or with probes 68a and 68b is a suitable restriction (not shown) which is sufficiently small that the velocity of air drawn through the restriction from conduits 50a and 50b is of sonic magnitude. Accordingly, air flow rates are constant through the sample cells- 73a and 73b and do not vary substantially with any variations in the vacuum (i.e., absolute pressure) maintained by vacuum source 39.

These restrictions also have the result that the volume of air withdrawn from conduits 50a and 50b by sample lines 67a and 67b is sufficiently small that substantially no variations occur in the pressure in plenum chamber 41 as detected by sensor 51. However, because of this, pressure sensors 61a and 67b are preferably located in close proximity (as illustrated) to sample cells 73a and 73b, respectively, so that the pressure sensed by them is that associated with the air passing through the sample cells.

Infrared analyzers 59a and 59b constitute radiation absorption analyzer means which generically may be regarded as a type of spectrum analyzer and which may each be of a commercially available type responsive to the tracer material. Or they may be of construction described hereinbelow. In either case, each of analyzers 59a and 59b includes a source of infrared radiation which is periodic in character, an arrangement for directing the periodic radiation through the respective sample cell 73a, 73b and through a reference or comparison cell, and means responsive to changes in the pressure of a gas caused by differential absorption in the sample and reference cells. Thelatter pressureresponsive means provides an electrical signal via respective leads 79a and 79b to analog divider circuits 63a and 63b, respectively. Signals varying as a function of the air pressure are provided to circuits 63a and 63b from pressure detectors 61a and 61b by respective leads 81a and 81b.

Analog divider circuits 63a and 63b are of a type known to those skilled in the art. As each analog divider circuit 63a, 63b receives the tracer partial pressure signal on line 79a, 79b and air flow signal on line 81a, 81b, the circuit calculates an air-fuel ratio, providing a signal representative of this ratio on a respective output lead 83a, 83b for operation of meters 65a and 65b.

Analog divider circuits 63a and 63b are each interconnectedwith lead 35. Any variations in the concentration of tracer material in fuel 16 are signalled by monitor circuitry 33 and the resultant signal on lead 35 causes circuits 63a and 63b to compensate for this variation by correcting accordingly the fuel-air ratio output signal provided on output leads 83a and 83b.

The outputs of analog dividers 63a and 63b are connected to meters 65a and 65b through a reversing switch 85 having a normal position interconnecting output lead 83a with meter 65a and output lead 83b with meter 65b. Switch 85 has also a reverse position interconnecting output lead 83a with meter 65b and output lead 83b with meter 65a. This arrangement facilitates cross-checking of the meters and determination of whether differences in their readings may be attributable to error in their operation. It is now apparent that valve 69 similarly permits cross-checking of the operation of analyzers 59a and 59b and calibration.

It will be understood that the output signal from analog dividers 63a and 63b may also be supplied to suitable recorders (not shown) or to digital voltmeters (not shown). Representative leads for these purposes are indicated at 87a, 87b and 89a, 89b.

It is significant to note that, in addition to providing signals representative of air-fuel ratios, analog dividers 63a and 63b may include provision for multiplying the respective tracer and air quantity input signals by suitable scale constants. In this way dividers 63a and 63b may provide additional output signals representative of the rates of air flow and fuel flow through the carburetor and which are displayed by suitable additional meters (not shown).

While pressure detectors 61a and 61b may, as noted, be of the type directly responsive to absolute, or total, gas pressure in lines 71a and 71b, they may instead advantageously comprise so-called polarographic oxygen partial pressure sensors of the type disclosed in an article by G. A. Rost in Aerospace Medicine, vol. 41, no. 8, August, 1970. Such sensors are responsive solely to the partial pressure of oxygen in a gas mixture. Since the ratio of oxygen in atmospheric air does not vary substantially, detection of the oxygen partial pressure by the sensors provides an extremely accurate measurement of the quantity of air in the fuel-air mixture flowing from the evaporator 49. When a small polarizing voltage is applied across electrodes of a polarographic sensor of this type, the sensor produces a current which is proportional to the partial pressure of oxygen.

In operation, the system of FIG. I quickly and accurately provides determination of the air-fuel ratios produced by a four-barrel or other multi-throat carburetor under conditions representative of normal operation of the carburetor. The carburetor 11 is placed on flow stand 11 and fuel line 17 is connected to fill the fuel bowl of the carburetor. The throttle is set to a desired opening as explained previously and vacuum source 39 and plenum 41 establish an air flow through one or more throats of the carburetor, as appropriate.

When the fuel bowl of the carburetor is filled, air-fuel mixture flow from the carburetor reaches a steady state condition. The flow is divided into two streams by the two halves of evaporator 49. Evaporator 49 evaporates the tracer material from the air-fuel mixture in each stream and separates liquid fuel from the air-fuel mixture in each stream to provide an air flow including the tracer material in gaseous form. A portion of the flow in each stream is withdrawn from conduits 50a and 50b for sampling by analyzers 59a and 59b.

The analyzers detect the partial pressure and thus the concentration of the gaseous tracer material for each of the two streams, providing signals which are functions of this concentration to analog dividers 63a and 63b. The partial pressure of air flowing in the two streams is detected by pressure detectors 61a and 61b (which may be polarographic oxygen sensors, as noted) and thus signals representative of the air quantity in the two streams are also provided to the analog dividers.

Analog dividers 63a and 63b effectively compare the partial pressures of the tracer material and of the air for the corresponding flow streams and derive the air-fuel ratios for the respective streams, each air-flow ratio being displayed by the appropriate one of meters 65a and 65b. The system responds very quickly, e.g., in the order of a few seconds, and thus it may quickly be ascertained that the carburetor is satisfactory or must be rejected, or necessary adjustments made. Since there may be several throttle settings and possibly several adjustments, the ability of the system to indicate quickly and accurately the air-fuel ratios for each side (or each throat) is highly advantageous, greatly reducing the amount of time required for testing each manufactured carburetor.

Referring now to FIG. 2, carburetor flow testing apparatus of the invention is illustrated which has improved speed of response. That is, the apparatus provides extremely rapid, substantially dynamic determination of the air-fuel ratios produced by a carburetor under test.

The apparatus includes a test stand 1 1' which may be similar to test stand 11 shown in FIG. 1 or may be of a type as disclosed in the before-mentioned copending application of Jean Bordeaux but including in any case an evaporator-separator or, simply, evaporator 49' (sometimes referred to as a vaporizer). A carburetor 13 is shown mounted to test stand 11, fuel including a tracer material in a predetermined percentage being supplied to the carburetor via a fuel line 17 of a suitable fuel distribution system like that represented in FIG. 1.

Associated with evaporator 49 is an air pressure detector or transducer 51 responsive to the air pressure in evaporator 49. This pressure, like the pressure in plenum chamber 41 of FIG. 1, is a direct function of the volume of air flowing per unit of time through carburetor 13. This pressure relationship results from sonic nozzles 45 through which vacuum source 39 withdraws air from the evaporator 49, which functions, of course, to evaporate or vaporize tracer material and separate liquid fuel from the air-fuel mixture thereby to provide an air flow including the tracer material in gaseous form.

As in FIG. 1, transducer 51 is interconnected with pressure conversion circuitry 52 which drives meter 53 to provide display of the air flow in weight or volumetric units, as in cubic feet per minute.

A sample tube or conduit 67' withdraws from evaporator 49' a portion of the air flow (including the gaseous tracer) for analysis by a radiation analyzer cell 73', preferably the sample cell of an infrared analyzer. The sampled gas is drawn through the analysis or sample cell by virtue of a conduit 77 interconnecting cell 73' in the vacuum line 37.

In accordance with the invention, sample conduit 67' provides relatively little restriction so as to cause relatively rapid flow of sampled gas from the air-flow through sample cell 73. Accordingly, the sample cell fills quickly, permitting the air (i.e., gas mixture) therein to be analyzed almost immediately following any change in the operation of carburetor 11. Air is thus withdrawn from evaporator 49 through sample line 67' at a much greater rate than in the apparatus of FIG. 1. Accordingly, the pressure detected by transducer 51 will be reduced and so will not accurately reflect the volume of air flowing through the carburetor. It is necessary, therefore, to correct the air measure ment.

For this purpose, a polarographic oxygen partial pressure analyzer 61' of the type discussed previously communicates with sample line 67 at a point closely adjacent sample cell 73'. Associated with oxygen detector or sensor 61' is appropriate circuitry 93 for supplying polarizing voltage for sensor 61 and amplifying the sensors output signal.

The oxygen detector circuit 93 provides signals to pressure compensation circuitry 95 and to an analog divider 63' like that shown in FIG. 1 which signals vary as a function of the oxygen partial pressure sensed by sensor 61'. The compensation circuit provides a pressure compensation signal to pressure conversion circuit 52 for causing the air quantity (volumetric) indication provided by meter 53 to be increased as a function of any increase in the oxygen partial pressure.

In this way, the increased volumetric flow of air through sample cell 73', while it may reduce the pressure in evaporator 49, is detected and utilized to correct the reading derived from transducer 51' and displayed by meter 53 which otherwise could be erroneously low. Itmay be noted that there will tend to be a constant rate of air flow through cell 73. Hence, once the operation of oxygen sensor 61' has stabilized, its output signal will tend to remain constant.

As a result, the short term rate of response of oxygen sensor 61' need not be vary fast. However, variations in the partial pressure (i.e., concentration) of the tracer material in the air flow passing through detector cell 73', resulting from variations in the air-fuel ratio produced by the carburetor, will be quickly detected by cell 73' and converted by the tracer detector circuitry 91 associted with cell 73 and supplied as a signal to analog divider 63'. Divider 63' operates as explained with regard to FIG. 1 to effectively compare the signals representative of the oxygen and tracer partial pressures and to derive from this comparison an air-fuel ratio which is displayed by meter 65'.

Referring now to FIGS. 3 and 4, infrared analysis apparatus useful for determining air-fuel ratios is illustrated which minimizes interference by vapor-form fuel. The problem of interference may be understood by noting that a fuel such as Stoddards solvent useful for carburetor flowing is a complex mixture of a large number of hydrocarbons. Each compound of this mixture has its own distinctive infrared absorption spectrum. Moreover, other solvents containing high proportions of aromatic compounds may be added to Stoddards solvent to adjust its viscosity.

These additive solvents may be compounds which have many sharp infrared absorption bands in a region of the infrared spectrum in which analysis of the tracer material is desirably carried out. Generally speaking, however, the resulting infrared absorption of variable blends of solvents or additives with Stoddards solvent is a complex grouping of sharp bands and general background absorption.

In the analysis or sample cell of an infrared analyzer, the absorption bands of such solvent mixture vapors overlap and thus interfere with the absorption bands of the tracer material, such as the fluorocarbon Freon 113, to an extent dependent upon the solvent mixture composition, pressure, and temperature. Such interference degrades the precision of analysis with the result that accuracy in thedetermination of air-fuel ratios, and stability and repeatability of results are reduced.

Improved infrared analysis apparatus in accordance with the present invention is indicated generally at 101. Such apparatus is advantageously employed in the flow-testing systems of FIGS. 1 and 2. Apparatus 101 includes a detector 102. Associated with the detector is a source of periodic infrared radiation, here illustrated as an infrared radiation element 103, energized for this purpose by a pulsed voltage soucre 105 or the like providing pulses at a frequency of 5 Hz, for example. Element 103 radiates a single beam of pulsed infrared radiation of predetermined wavelength (i.e., a band or predetermined continuum of infrared energy) which is directed through a front optical window 107, through a sample cell or chamber 109, through an inner optical window 111, and thence through a reference cell or chamber 113. The optical length of sample cell 109 is much shorter than that of reference cell 113. Gas to be sampled is admitted to sample cell 109 by air inlet conduit and discharged therefrom by an outlet conduit 117.

While the details and materials of construction of detector 102 are matters which will be within the knowledge or ability of those skilled in the design of infrared radiation analyzers, it is important to note here that detector 102 includes a so-called back chamber 119 closed by a lid 121 and including suitable provision such as recesses 123 and 125 in which are positioned respective diaphragm assemblies 127 and 129.

A port 131 provides pressure communication betweeen one side of diaphragm assembly 127 and sample cell 109 and a similar port 133 provides communication between one side of diaphragm assembly 129 and reference cell 113. Pressure in back chamber 119 acts on the otherside of each of the diaphragm assemblies which are preferably of a construction similar to that used in other types of infrared analyzers.

Assemblies 127 and 129 each include a thin gold leaf diaphragm which is movable with respect to a fixed electrode spaced a small distance, e.g., 0.003 in., from the diaphragm to provide, in'effect avariable capacitor whose capacitance varies with changes in pressure causing movement of the diaphragm. Suitable feedthrough terminals 135 and 137 provide respective interconnections with one of the electrodes of each diaphragm assembly, the body of detector 102 (which may be of brass) providing the other. Terminals 135 and 137 are interconnected with conventional electronic circuitry for converting the capacitance variations into a signal which varies as a function of the concentration of a gas being sampled by sample cell 109 by amplification, filtering, demodulating and conditioning.

In operation of detector 102, both reference chamber or cell 113 and back chamber 119 are filled with a sensitizing gas having fuel (e.g., Stoddards solvent) vapor components of the type which would cause absorption interference with the tracer vapor to be detected. It will be understood that inlet conduit 115 is connected for sampling the air flow from evaporator 49 of FIG. 1 or 49' and thus is connected in the same manner as sample conduits 67a, 67b or 67 of FIGS. 1 and 2. Conduit 117 is connected to a vacuum source and thus the gas mixture, i.e., air flow from the evaporator, including the gaseous or vapor tracer material is drawn through sample cell 109.

During the portion of each radiation pulse cycle during which infrared radiation passes through sample cell 109 and then through reference cell 113, absorption of the radiation by the gas in cells 109 and 113 produces a small temperature rise of the gas and thereby resulting in a slight pressure increase causing the diaphragm to deflect toward the fixed electrode in the respective diaphragm assembly 127 and 129. During the portion of the cycle in which the beam is absent, the temperature and pressure return to their ambient values and each diaphragm returns to its original position.

Such expansion cycles are repeated at the Hz radiation pulse rate, the diaphragm deflection amplitude being directly dependent upon the amount of radiant energy absorbed by the sensitizing or so-called charge gas in reference cell 113. Maximum deflection occurs in the absence of tracer vapor in sample cell 109. As the concentration of the tracer (e.g., the fluorocarbon Freon 113)- increases in cell 109, the deflection amplitude and thus the capacitance variation of diaphragm assembly 127 is increased considerably while the capacitance variation of diaphragm assembly 129 is decreased only slightly.

While diaphragm assembly 127 detects pressure changes in sample cell 109 resulting from absorption of radiation by the tracer vapor, fuel vapors present in cell 109 also induce pressure changes by absorption of the radiation in a sense tending to interfere with the detecting of pressure changes resulting from tracer absorption.

Diaphragm assembly 129 detects pressure changes in reference cell 113 resulting from absorption of the radiation by the concentration of fuel or solvent vapors therein. However, the back chamber arrangement substantially cancels the detected pressure changes in the sample cell resulting from the interfering vapor-form fuel with the detected pressure changes in the reference cell.

Accordingly, it is seen that sample cell 109 and its diaphragm assembly 129 constitute a first radiation detector means responsive to the partial pressure of the tracer material in the air flow from the flow stand evaporator which is sampled. Similarly, reference cell 113 and its associated diaphgram assembly 129 constitute second radiation detector means responsive to a predetermined fuel vapor concentration, the second detector means being operatively associated by means of back chamber 119 with the first detector means for causing cancellation of the interference by the vapor-form fuel in the sampled air flow.

It will be understood that, when detector 102 is used for determination of air-fuel ratios, the flow-testing apparatus includes a suitable pressure sensor responsive to the partial pressure of air in the air flow from the evaporator as well as analog divider means responsive to signals from this sensor and from the radiation analyzer electronics for effectively comparing the air and tracer partial pressures to derive the air-fuel mixture produced by the carburetor under test.

F IG. 4 illustrates a modified version 102 of the detector shown in FIG. 3, and providing what may be termed a flow-through radiation analyzer embodiment 101.

It will be understood that, when detector 102 is used for determination of air-fuel ratios, the flow-testing apparatus includes suitable pressure sensor responsive to the partial pressure of air in the air flow from the evaporator as well as analog divider means responsive to signals from this sensor and from the radiation analyzer electronics for effectively comparing the air and tracer partial pressures to derive the air-fuel mixture produced by the carburetor under test. Detector 102', in addition to minimizing fuel vapor interference, is adapted to provide extremely rapid, substantially dynamic determination of air-fuel ratios produced by a carburetor under test.

Detector 102' is shown to include a sample cell 109' which is constituted, in effect, by a portion 137 of a conduit which may be assumed to constitute the downstream end or an extension of an evaporator of the type shown in FIGS. 1 and 2. In this context, it will be understood that the evaporator operates as described previously to evaporate the tracer material from the air-fuel mixture flowing from the carburetor and to separate liquid fuel from the mixture to provide an air flow including the tracer material in gaseous, i.e., vapor form, and including also any fuel which may have evaporated.

This air flow from the evaporator enters conduit 137 as indicated by a legend and arrow in the drawing, flows through sample cell 109, and then exits via a discharge conduit portion 139 connected, as by means of a plenum (as in FIG. 1) to the vacuum source. Conduit 137 is shown to include a suitable front window 107 permitting the beam of periodic infrared radiation from source 103 to pass through the sample cell 109', then through a suitable inner window 111' separating the sample cell 109 from a reference chamber or cell 1 l3, and finally through the reference cell. The detector is shown to include a modified port or passage 131' providing communication between cell 109 and diaphragm assembly 127.

Thus, it will be seen that the partial pressure of tracer vapor in sample cell will be detected immediately and without delay in filling the sample cell as required in FIGS. 1 and 3. At 61' is represented a polarographic oxygen partial pressure sensor of the type described with regard to FIG. 2 and which is interconnected with suitable amplification circuitry for providing a signal representative of the partial pressure of the air of the air flow. Thediaphragm assemblies 127 and 129 of detector 102' are, of course, connected to the conventional analyzer circuitry to provide a signal representative of the partial pressure of tracer in the air flow. As described, analog divider means divides one signal by the other to provide a third signal representative of the air-fuel ratio produced by the carburetor under test.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising:

means for establishing flow of air through the carburetor;

means for supplying liquid fuel to the carburetor for producing a flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage;

tracer detector means for detecting the concentration of tracer material in said flow from the carburetor; oxygen detector means for detecting the concentration of oxygen in said flow from the carburetor; and

means for deriving from the detected tracer and oxygen concentrations the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by said carburetor.

2. Apparatus as set forth in claim 1 wherein said tracer detector means is responsive to the partial pressure in the flow from said carburetor.

3. Apparatus as set forth in claim 2 wherein said oxygen detector means comprises a polarographic sensor responsive to the partial pressure of oxygen.

4. Apparatus as set forth in claim 2 wherein said tracer detector means comprises a radiation analyzer including a radiation source, means for directing the radiation through at least a portion of said flow from the carburetor, and means responsive to absorption of said radiation by tracer material in said flow from the carburetor.

5. Apparatus as set forth in claim 4 wherein said radiation is directed across said flow from the carburetor.

6. Apparatus as set forth in claim 5 wherein said means for establishing flow of air through the carburetor includes a conduit interconnecting the carburetor with a vacuum source, said radiation being directed across the flow in said conduit.

7. Apparatus as set forth in claim 6 wherein said radiation analyzer is an infrared analyzer and said means responsive to absorption comprises a pressure detector responsive to changes in the pressure in the flow in said conduit resulting from absorption of infrared radiation by the tracer material.

8. Apparatus as set forth in claim 4 wherein said radiation analyzer includes a sample cell for sampling said flow from the carburetor, said apparatus comprising means for causing rapid sampling of flow from the carburetor by said cell.

9. Apparatus as set forth in claim 8 including an air pressure detector for detecting the rate of air flowing through the carburetor, said rapid sampling by said cell inducing error in the detected rate of air flow by said pressure detector, said apparatus further comprising means responsive to said oxygen detector means for correcting said error.

10. Apparatus as set forth in claim 9 wherein said oxygen detector means comprises a polarographic sensor associated with said sampling cell and responsive to the partial pressure of oxygen in the flow sampled by said cell. I

ll. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising:

means for establishing flow of air through the carburetor;

means for supplying liquid fuel to the carburetor for producing flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage;

means for evaporating said tracer material from said mixture and for separating substantial liquid fuel from said mixture to provide an air flow containing said tracer material in gaseous form;

radiation analyzer means responsive to the partial pressure of tracer material in said air flow;

oxygen sensor means responsive to the partial pressure of oxygen in said air flow; and

means for deriving from the detected tracer material and oxygen concentrations the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by said carburetor.

12. Apparatus as set forth in claim 11 wherein said radiation analyzer means provides a first signal which is a function of the tracer material partial pressure, said oxygen sensor means provides a second signal which is a function of the oxygen partial pressure, and said means for deriving the air-fuel ratio comprises means for dividing said second signal by said first signal to obtain a third signal representative of air-fuel ratio.

13. The method of flow-testing a carburator to determine air-fuel ratios produced by the carburetor under conditions representative of normal operation thereof comprising:

establishing flow of air through the carburetor;

supplying liquid fuel including a tracer material to the carburetor for producing a flow of an air-fuel mixture from the carburetor;

detecting the partial pressure of oxygen in said flow;

detecting the partial pressure of tracer material in said flow; and electronically comparing said partial pressures to derive the air-fuel ratio produced by the carburetor. 14. The method as set forth in claim 13 including the steps of:

generating a first signal representative of the partial pressure of oxygen in said flow; and generating a second signal representative of the partial pressure of tracer material in said flow; said electronically comparing said partial pressures comprising dividing said first signal by said second signal to obtain a third signal representative of the air-fuel ratio produced by the carburetor. 15. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof,

comprising:

means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage; means for evaporating said tracer material from said mixture and for separating substantial liquid fuel from said mixture to provide an air flow containing said tracer material in gaseous form but including some of said fuel in vapor form; radiation absorption analyzer means including first radiation detector means responsive to the partial pressure of tracer material in gaseous form in said air flow, said fuel in vapor form in said air flow causing interference with the response to the quantity of tracer material, and second radiation detector means responsive to a predetermined vapor concentration of said fuel and operatively associated with said first detector means for causing cancellation of the interference by vapor-form fuel in said air flow; pressure sensor means responsive to the partial pressure of air in the air flow; and

means for comparing the partial pressures of said tracer material and of the air of said air flow and deriving from the compared partial pressures an air-fuel ratio of the air-fuel mixture produced by the carburetor.

16. Apparatus as set forth in claim 15 wherein said first radiation detector means comprises a first detector cell and first pressure detector means responsive to the gas pgressure in said first cell, and said second detector means comprises a second detector cell and second pressure detector means responsive to the gas pressure in said second cell, said pressure detector means being differentially responsive to changes in pressure in said second cell.

17. Apparatus as set forth in claim 17 further comprising a chamber including a gas therein, each of the pressure detector means being operatively associated with the gas in said chamber.

18. Apparatus as set forth in claim 18 wherein each of said pressure detector means comprises a diaphragm, each having one side exposed to gas pressure in a respective one of said cells and each diaphragm having the other side exposed to gas pressure in said chamber.

19. Apparatus as set forth in claim 18 wherein said chamber and said second cell are filled with the same gas.

20. Apparatus as set forth in claim 19 wherein the last-said gas comprises at least in part vapor of said fuel.

21. Apparatus as set forth in claim 16 wherein the means for establishing flow of air through the carburetor comprises a conduit interconnecting the downstream side of the carburetor with a vacuum source, said first cell being constituted by said conduit.

22. The method of flow-testing a carburetor for determining air-fuel ratios produced by said carburetor under conditions representative of normal operation thereof, comprising:

establishing flow of air through the carburetor;

adding to liquid fuel a predetermined percentage of tracer material;

supplying the liquid fuel including the tracer material to the carburetor for causing the throats thereof to produce flow of an air-fuel mixture fromthe carburetor;

evaporating said tracer material from the air-fuel mixture;

separating liquid fuel from the air-fuel mixture to provide an air flow including said tracer material in gaseous form, some of said fuel tending to remain in vapor form in said air flow; directing a source of periodic radiation through gases of said air flow in a radiation detector cell;

detecting pressure changes in said cell resulting from absorption of said radiation by said tracer material, the presence of said vapor-form fuel causing also changes in pressure resulting from absorption of said radiation by said vapor-form fuel and thereby interfering with said detecting of pressure changes;

directing said radiation also through a predetermined concentration of vapor-form fuel in a further detector cell;

detecting pressure changes in the further detector cell resulting from absorption of said radiation by the concentration of vapor-form fuel therein;

cancelling substantially the detected pressure changes in the first cell resulting from the interfering vapor-form fuel therein with the detected pressure changes in the second cell thereby to detect from said pressure changes the partial pressure of the gaseous tracer material in said air stream;

detecting the partial pressure of air flowing in said air stream;

comparing the partial pressures of said gaseous tracer material and of the air flowing in said air stream; and

deriving from the compared partial pressures an airfuel ratio of the air-fuel mixture produced by the carburetor.

23. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising:

means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing a flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage;

first detector means sampling said flow from the carburetor for detecting the concentration of tracer material in said flow from the carburetor; second detector means for detecting the quantity of air flowing in said flow from the carburetor;

means for deriving from the detected tracer concentration and air quantity the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by the carburetor; and

means for increasing the speed of sampling by said first detector means thereby to provide rapid determination of the air-fuel ratio produced by the carburetor.

24. Apparatus as set forth in claim 23 wherein said first detector means is responsive to the partial pressure in the flow from said carburetor.

25. Apparatus as set forth in claim 24 wherein said second detector means comprises a polarographic sensor responsive to the partial pressure of oxygen in said flow from the carburetor.

26. Apparatus as set forth in claim 24 wherein said first detector means comprises a radiation analyzer including a radiation source, means for directing the radiation through at least a portion of said flow from the carburetor, and means responsive to absorption of said radiation by tracer material in said flow from the carburetor.

27. Apparatus as set forth in claim 26 wherein said radiation is directed across said flow from the carburetor.

28. Apparatus as set forth in claim 27 wherein said means for establishing flow of air through the carburetor includes a conduit interconnecting the carburetor with a vacuum source, said radiation being directed across the flow in said conduit.

29. Apparatus as set forth in claim 22 including an air pressure detector for detecting the rate of air flowing through the carburetor, said increased speed of sampling inducing error in the detected rate of air flow by said pressure detector, said apparatus further comprising means responsive to said second detector means for correcting said error.

30. Apparatus as set forth in claim 29 wherein said second detector means comprises a polarographic sensor associated with said first detector means and re sponsive to the partial pressure of oxygen in the flow sampled by said first detector means.

i i 1' i i 

1. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising: means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing a flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage; tracer detector means for detecting the concentration of tracer material in said flow from the carburetor; oxygen detector means for detecting the concentration of oxygen in said flow from the carburetor; and means for deriving from the detected tracer and oxygen concentrations the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by said carburetor.
 2. Apparatus as set forth in claim 1 wherein said tracer detector means is responsive to the partial pressure in the flow from said carburetor.
 3. Apparatus as set forth in claim 2 wherein said oxygen detector means comprises a polarographic sensor responsive to the partial pressure of oxygen.
 4. Apparatus as set forth in claim 2 wherein said tracer detector means comprises a radiation analyzer including a radiation source, means for directing the radiation through at least a portion of said flow from the carburetor, and means responsive to absorption of said radiation by tracer material in said flow from the carburetor.
 5. Apparatus as set forth in claim 4 wherein said radiation is directed across said flow from the carburetor.
 6. Apparatus as set forth in claim 5 wherein said means for establishing flow of air through the carburetor includes a conduit interconnecting the carburetor with a vacuum source, said radiation being directed across the flow in said conduit.
 7. Apparatus as set forth in claim 6 wherein said radiation analyzer is an infrared analyzer and said means responsive to absorption comprises a pressure detector responsive to changes in the pressure in the flow in said conduit resulting from absorption of infrared radiation by the tracer material.
 8. Apparatus as set forth in claim 4 wherein said radiation analyzer includes a sample cell for sampling said flow from the carburetor, said apparatus comprising means for causing rapid sampling of flow from the carburetor by said cell.
 9. Apparatus as set forth in claim 8 including an air pressure detector for detecting the rate of air flowing through the carburetor, said rapid sampling by said cell inducing error in the detected rate of air flow by said pressure detector, said apparatus further comprising means responsive to said oxygen detector means for correcting said error.
 10. Apparatus as set forth in claim 9 wherein said oxygen detector means comprises a polarographic sensor associated with said sampling cell and responsive to the partial pressure of oxygen in the flow sampled by said cell.
 11. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising: means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage; means for evaporating said tracer material from said mixture and for separating substantial liquid fuel from said mixture to provide an air flow containing said tracer material in gaseous form; radiation analyzer means responsive to the partial pressure of tracer material in said air flow; oxygen sensor means responsive to the partial pressure of oxygen in said air flow; and means for deriving from the detected tracer material and oxygen concentrations the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by said carburetor.
 12. Apparatus as set forth in claim 11 wherein said radiation analyzer means provides a first signal which is a function of the tracer material partial pressure, said oxygen sensor means provides a second signal which is a function of the oxygen partial pressure, and said means for deriving the air-fuel ratio comprises means for dividing said second signal by said first signal to obtain a third signal representative of air-fuel ratio.
 13. The method of flow-testing a carburator to determine air-fuel ratios produced by the carburetor under conditions representative of normal operation thereof comprising: establishing flow of air through the carburetor; supplying liquid fuel including a tracer material to the carburetor for producing a flow of an air-fuel mixture from the carburetor; detecting the partial pressure of oxygEn in said flow; detecting the partial pressure of tracer material in said flow; and electronically comparing said partial pressures to derive the air-fuel ratio produced by the carburetor.
 14. The method as set forth in claim 13 including the steps of: generating a first signal representative of the partial pressure of oxygen in said flow; and generating a second signal representative of the partial pressure of tracer material in said flow; said electronically comparing said partial pressures comprising dividing said first signal by said second signal to obtain a third signal representative of the air-fuel ratio produced by the carburetor.
 15. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising: means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage; means for evaporating said tracer material from said mixture and for separating substantial liquid fuel from said mixture to provide an air flow containing said tracer material in gaseous form but including some of said fuel in vapor form; radiation absorption analyzer means including first radiation detector means responsive to the partial pressure of tracer material in gaseous form in said air flow, said fuel in vapor form in said air flow causing interference with the response to the quantity of tracer material, and second radiation detector means responsive to a predetermined vapor concentration of said fuel and operatively associated with said first detector means for causing cancellation of the interference by vapor-form fuel in said air flow; pressure sensor means responsive to the partial pressure of air in the air flow; and means for comparing the partial pressures of said tracer material and of the air of said air flow and deriving from the compared partial pressures an air-fuel ratio of the air-fuel mixture produced by the carburetor.
 16. Apparatus as set forth in claim 15 wherein said first radiation detector means comprises a first detector cell and first pressure detector means responsive to the gas pgressure in said first cell, and said second detector means comprises a second detector cell and second pressure detector means responsive to the gas pressure in said second cell, said pressure detector means being differentially responsive to changes in pressure in said second cell.
 17. Apparatus as set forth in claim 17 further comprising a chamber including a gas therein, each of the pressure detector means being operatively associated with the gas in said chamber.
 18. Apparatus as set forth in claim 18 wherein each of said pressure detector means comprises a diaphragm, each having one side exposed to gas pressure in a respective one of said cells and each diaphragm having the other side exposed to gas pressure in said chamber.
 19. Apparatus as set forth in claim 18 wherein said chamber and said second cell are filled with the same gas.
 20. Apparatus as set forth in claim 19 wherein the last-said gas comprises at least in part vapor of said fuel.
 21. Apparatus as set forth in claim 16 wherein the means for establishing flow of air through the carburetor comprises a conduit interconnecting the downstream side of the carburetor with a vacuum source, said first cell being constituted by said conduit.
 22. The method of flow-testing a carburetor for determining air-fuel ratios produced by said carburetor under conditions representative of normal operation thereof, comprising: establishing flow of air through the carburetor; adding to liquid fuel a predetermined percentage of tracer material; supplying the liquid fuel including the tracer material to the carburetor for causing the throats thereof to produce flow of an aiR-fuel mixture from the carburetor; evaporating said tracer material from the air-fuel mixture; separating liquid fuel from the air-fuel mixture to provide an air flow including said tracer material in gaseous form, some of said fuel tending to remain in vapor form in said air flow; directing a source of periodic radiation through gases of said air flow in a radiation detector cell; detecting pressure changes in said cell resulting from absorption of said radiation by said tracer material, the presence of said vapor-form fuel causing also changes in pressure resulting from absorption of said radiation by said vapor-form fuel and thereby interfering with said detecting of pressure changes; directing said radiation also through a predetermined concentration of vapor-form fuel in a further detector cell; detecting pressure changes in the further detector cell resulting from absorption of said radiation by the concentration of vapor-form fuel therein; cancelling substantially the detected pressure changes in the first cell resulting from the interfering vapor-form fuel therein with the detected pressure changes in the second cell thereby to detect from said pressure changes the partial pressure of the gaseous tracer material in said air stream; detecting the partial pressure of air flowing in said air stream; comparing the partial pressures of said gaseous tracer material and of the air flowing in said air stream; and deriving from the compared partial pressures an air-fuel ratio of the air-fuel mixture produced by the carburetor.
 23. Carburetor flow-testing apparatus for determining air-fuel ratios produced by a carburetor under conditions representative of normal operation thereof, comprising: means for establishing flow of air through the carburetor; means for supplying liquid fuel to the carburetor for producing a flow of an air-fuel mixture from the carburetor, said fuel containing a tracer material in a predetermined percentage; first detector means sampling said flow from the carburetor for detecting the concentration of tracer material in said flow from the carburetor; second detector means for detecting the quantity of air flowing in said flow from the carburetor; means for deriving from the detected tracer concentration and air quantity the air-fuel ratio of said mixture and thereby the air-fuel ratio produced by the carburetor; and means for increasing the speed of sampling by said first detector means thereby to provide rapid determination of the air-fuel ratio produced by the carburetor.
 24. Apparatus as set forth in claim 23 wherein said first detector means is responsive to the partial pressure in the flow from said carburetor.
 25. Apparatus as set forth in claim 24 wherein said second detector means comprises a polarographic sensor responsive to the partial pressure of oxygen in said flow from the carburetor.
 26. Apparatus as set forth in claim 24 wherein said first detector means comprises a radiation analyzer including a radiation source, means for directing the radiation through at least a portion of said flow from the carburetor, and means responsive to absorption of said radiation by tracer material in said flow from the carburetor.
 27. Apparatus as set forth in claim 26 wherein said radiation is directed across said flow from the carburetor.
 28. Apparatus as set forth in claim 27 wherein said means for establishing flow of air through the carburetor includes a conduit interconnecting the carburetor with a vacuum source, said radiation being directed across the flow in said conduit.
 29. Apparatus as set forth in claim 22 including an air pressure detector for detecting the rate of air flowing through the carburetor, said increased speed of sampling inducing error in the detected rate of air flow by said pressure detector, said apparatus further comprising means responsive to said second detector means for correcting said error.
 30. Apparatus as set Forth in claim 29 wherein said second detector means comprises a polarographic sensor associated with said first detector means and responsive to the partial pressure of oxygen in the flow sampled by said first detector means. 